League is a noun. It means a group. League is a covenant or association of individuals or parties or states, etc who has the common goal and interest. The synonyms of league are Alliance, confederation, coalition, group, etc. The first use of this word was done in 15th century from the French word ligue. However, league can also be a unit to measure the length usually while at sea. It is not an official unit of measurement in any nation was long common in practice in Europe and Latin America. The word basically is intended to say the distance a person could walk in an hour. 

The word league is more common in football matches at present with no use in measuring the length. There are several league matches being held in the world basically league associated with football is very popular in the world. UEFA Champions League,Spanish Premier League, English Premier League, etc are very famous forms of league matches in the world.